Not applicable.
Not applicable.
The field of the invention is power converters and more specifically converter configurations including heat sinks that reduce the overall space required to accommodate the configurations.
It is well known that variable speed drives of the type used to control industrial electric motors include numerous electronic components. Among the various electronic components used in typical variable-speed drives, all generate heat to a varying degree during operation. Typically, high-power switching devices such as IGBTs, diodes, SCRs and the like as well as storage devices such as capacitors are responsible for generating most of the heat in a variable-speed drive. It is for this reason, therefore, that most variable-speed drives include a heat sink(s) upon which the power switching devices are mounted. The heat sink(s) conducts potentially damaging heat from assembly components.
Selecting the size and design of a heat sink for a particular variable speed drive is somewhat of a challenge. First, a designer must be aware of the overall characteristics of the motor and drive pair. Second, the designer must understand the industrial application in which the motor and drive pair will be used, including the continuous and peak demands that will likely be placed on the motor and drive by the load. Third, the designer must accommodate, in the design, certain unexpected conditions that would deleteriously affect the heat transfer capability of the heat sink such as unexpectedly high ambient temperatures, physical damage to the heat sink such as mechanical damage, or a build up of a debris layer, as examples. Fourth, the heat sink(s) must be physically dimensioned so as to fit into the space allotted per customer requirements, cabinet or enclosure size, or the like.
In the past, air-cooled heat conducting plates were used to transfer thermal energy from electronic parts to the ambient air. These were passive heat-transfer devices and were generally formed of a light-weight aluminum extrusion including a set of fins. As a general rule, heat transfer effectiveness is based on the temperature differential between the power devices and the ambient air temperature. Of course, in order to provide adequate heat conduction, heat sinks of this type oftentimes are necessarily large and, therefore, bulky and expensive. If high ambient conditions exist, the heat sink becomes ineffective or useless as heat removal cannot be accomplished regardless of the size of the heat sink. If the variable speed drive was in an enclosed space the heat removed from the drive would need to be exhausted or conditioned for recirculation.
By forcing air over fins defined on the heat-conducting plate (e.g., an aluminum extrusion), improved cooling efficiency can be realized. Large blower motors are often used for this purpose. However, as the fins defined in the aluminum extrusions become dirty or corroded during use, the heat sinks become less effective or useless altogether. Blower motors cannot be used in environments where air cleanliness would clog filtration. Therefore, air conditioning equipment is often added to internally circulate and cool the air that is passed over the heat sink fins.
Liquid cooled heat sinks or cold plates have also been used for some applications but with limited success. Generally, a liquid cooled heat sink includes a series of chambers or channels that are formed internally within a sink body member that is formed of material (e.g., copper or aluminum) that readily conducts heat. The body member includes at least one mounting surface for receiving heat generating devices. The channels are typically configured so that at least one channel section is formed adjacent each surface segment to which a heat generating device is mountedxe2x80x94typical channel configurations are serpentine. A coolant liquid is pumped through the channels from one or more inlet ports to one or more outlet ports to cool the sink member and hence conduct heat away form the heat generating devices.
The industry has developed several ways in which to manufacture liquid cooled heat sinks and, each of the different ways to manufacture has different costs associated therewith. For instance, a liquid cooled sink can be constructed by forming a desired serpentine copper conduit path for liquid flow, placing the serpentine conduit construct within a sink mold, pouring molten liquid aluminum into the mold and allowing the molten aluminum to cool. While this manufacturing process has been used successfully, liquid molding processes are very difficult to control and the incidences of imperfect and or non-functioning product have been relatively high.
One other sink manufacturing process that has proven useful includes cutting a at least one channel out of a sink body member, hermetically sealing (e.g., vacuum brazing) a cover member to the body member to cover the channel and then forming an inlet and an outlet that open into opposite ends of the channel. This two part sealing process is much less expensive than the conduit-molten process described above.
When designing any liquid cooled heat sink several factors have to be considered including heat dissipating effectiveness, volume required to accommodate a resulting converter, and cost. With respect to heat dissipation, in the case of a power conversion assembly, there are typically several different heat generating devices that are similarly constructed and that operate in a similar fashion to convert power. For instance, as well known in the controls arts, an AC to DC rectifier typically includes a plurality of power switching devices that are arranged to form a bridge assembly. In the case of a three phase supply and load, the bridge assembly includes three phases, a separate switching phase for each of the three supply and load phases. Here, an exemplary phase may include first and second power switching devices linked at a common node to an associated supply line where the other terminals of the first and second switches are linked to positive and negative DC busses, respectively. A controller is configured to control all of the three phases of the bridge together to convert the three phase AC supply voltage to a DC potential across the positive and negative DC busses.
In a similar fashion, a three phase inverter assembly typically includes three separate phases that link positive and negative DC busses to three load supply lines. In the case of an inverter, each phase typically includes first and second power switching devices that are linked in series between the positive and negative DC busses with the common node between the first and second inverter switches linked to an associated phase of the load. Where the supply and load voltages are large, some rectifier/inverter converter assemblies may include several three phase bridges linked together thereby reducing the load handling of each switching device.
In the case of a rectifier-inverter conversion assembly, a drive circuit is provided that controls all of the switching devices together to create desired three phase output voltages to drive a load linked thereto. In this case, it is imperative that the switching devices operate in characteristic and substantially similar ways to simplify what is, by its very nature, an already complex switching scheme. For this reason, converter designers typically select switching devices having known operating characteristics to configure their conversion assemblies.
Nevertheless, as also well known, most switching devices have operating characteristics that are, at least in part, affected by the environments in which the devices operate. Specifically, for the purposes of the present invention, it should be appreciated that switching device operating characteristics change as a function of temperature. For instance, an internal switch resistance has been known to change as a function of temperature which in turn affects the voltage drop across the switch. While each voltage drop change that occurs may seem insignificant, because rectifier and inverter switches are typically turned on and off very rapidly, the affect of changing device drop has been shown to be appreciable.
The problems associated with voltage drop variance are compounded where similar switching devices are operated at different temperatures and is especially acute where control schemes operate to simultaneously control all three conversion assembly phases together to generate load voltages. Thus, for instance, where one switching device is several degrees hotter than another switching device, the result may be unbalanced phase voltages and hence imperfect load control (e.g., non-smooth motor rotation) which increases overall system wear and can cause system damage over time.
For this reason, one challenge when designing a heat sink for use with a converter assembly has been to provide essentially identical heat dissipating capacity to each converter switching device so that device temperatures are essentially identical during system operation. The problem here is that coolant temperature rises as the coolant absorbs heat along its path through a sink member so that power switching devices relatively near an inlet port along a serpentine coolant path are cooled to a greater degree than switching devices down stream from the inlet port. One solution that reduces the heat dissipating capacity differential between similar switching devices has been to provide a heat sink where the spacing between a cooling liquid inlet and each of the sink surfaces to which switching devices are mounted is similar. For instance, where a configuration includes twenty four power switching devices, instead of mounting the switching devices to the sink in a pattern that tracks a single serpentine cooling conduit path, the switching devices may be mounted on sink member mounting surface to form six rows of four switching devices each where each of the six rows is fed by a separate one of six liquid coolant inlet portsxe2x80x94here a manifold may serve each of the six inlet ports (see generally FIG. 23 in U.S. Pat. No. 6,031,751 (hereinafter xe2x80x9cthe ""751 patentxe2x80x9d) entitled xe2x80x9cSmall Volume Heat Sink/Electronic Assemblyxe2x80x9d which issued on Feb. 29, 2000 and which is incorporated herein by reference). Thus, in this case, coolant from each of the six inlet ports passes by four separate heat generating devices and device cooling will be relatively more uniform. This solution to reduce the device temperature differential will be referred to hereinafter as a matrix spacing solution.
One other solution that reduces the heat dissipating capacity differential between switching devices mounted to a sink member has been to provide a serpentine path that passes by each heat generating device more than once so that the overall cooling affect of devices is similar. For instance, assume twelve switching devices are mounted to a sink member mounting surface to form two rows of six devices each and that a single serpentine path is configured to include a first linear run that passes adjacent the first row of devices, a first 180 degree turn, a second linear run that passes adjacent the second row of devices, a second 180 degree turn, a third linear run that again passes adjacent the second row of devices, a third 180 degree turn and a fourth linear run that passes a second time by the first row of devices to an outlet.
Here, in theory, the first linear run should include the coolest coolant, the second linear run should include the second coolest coolant and so on so that the coolant temperatures through the first and fourth linear runs (i.e., adjacent the devices in the first row) should average and the coolant temperatures though the second and third linear runs (i.e., adjacent the devices in the second row) should also average and the two average temperatures should be similar (see generally FIG. 2 in the ""751 patent). This solution to reduce the device temperature differential will be referred to hereinafter as an averaging solution.
While the averaging solution and the matrix spacing solution work in theory, in reality, each of these solutions have had some problems regarding temperature differential. With respect to the matrix spacing solution, in the example above, the fourth device along each of the six separate coolant paths is warmer than the first device along the same path as liquid passing by the first three devices along the path heats up when heat is absorbed along the path. Thus, while better than sinks that align devices along a single serpentine cooling conduit path, the matrix solution still results in a temperature differential.
With respect to the averaging solution, it has been determined that, despite multi-pass designs, at least some temperature differential still exists between devices spaced at different locations along the coolant conduit path. In addition, in some cases, cooling capacity may vary over the heat dissipating surface of each heat generating device. This intra-device dissipating differential may occur as a multi pass path necessarily requires that the coolest pass (i.e., the first pass by a device) be positioned along one side of a dissipating surface so that another one or more passes that include relatively warmer coolant can be positioned along the other side of the dissipating surface.
With respect to volume (i.e., the second factor above to consider when designing a heat sink), as with most electronics designs, all other things being equal, smaller is typically considered better. Thus, some prior converter configurations have provided sink members that either facilitate stacking of relatively short devices adjacent elongated devices (see FIG. 19 in the ""751 patent) or, in the alternative, aligning similar dimensions of different devices (see FIG. 13 in the ""751 patent).
For instance, the ""751 patent recognizes that, in addition to power switching devices, converter configuration capacitors also often generate excessive heat that should be dissipated to ensure proper operation. The ""751 patent also recognizes that capacitors typically have a length dimension perpendicular to their heat dissipating surface that is much longer than the thickness dimensions of typical switching devices perpendicular to the device dissipating surfaces and that the switching devices typically have a length dimension that is similar to the capacitor length dimension. In this case, in one embodiment, the ""751 patent recognizes that overall converter configuration size can be reduced by providing an L shaped sink member having two legs that form a 90xc2x0 angle, mounting the capacitors to an inside surface of one of the legs and within the space defined by the two leg members and mounting the switching devices to the outside surface of the other of the leg members thereby aligning the similar capacitor and device length dimensions.
With respect to cost, unfortunately, where an L shaped heat sink member or, for that matter, where a sink member having sections that reside along other than a single plane is required to stack or align capacitors with switching devices, the relatively inexpensive two part sealing process described above becomes much more difficult to use. This is because the two part sealing process generally includes vacuum sealing a flat cover member over a channel forming body member, When the channel must reside in more than one plane and requires a more complex cover member, tolerances required to provide a suitable cover member would be extremely difficult to meet and the sealing process would be difficult to perform effectively.
Thus, where the sink member must reside in two or more planes to facilitate stacking and/or aligning, the more expensive molten-conduit process would likely be employed where the conduit is formed into the desired channel shape and molten aluminum or the like is poured into a mold there around. For this reason prior stacking and aligning configurations have proven to be relatively expensive to manufacture and often are not suitable given cost constraints.
Also, with respect to cost, often the last converter design consideration is how system components will be electrically linked together to form a converter topology. One particularly advantageous and robust type of linking assembly is referred to generally as a laminated bus bar. As its label implies, a laminated bus bar typically includes a plurality of metallic sheets of laminate that are layered together with insulators between adjacent laminate sheets. Vias are formed within the laminated assembly where links are to be made to capacitor and switching device terminals. The vias automatically link the devices and capacitors up in a desired fashion to provide an intended converter topology (e.g., rectifier, inverter, rectifier-inverter, etc.).
Laminated bus bar cost is generally a function of the amount of material required to construct the bus, the number of laminate layers required to support a configuration and the overall complexity of the required laminate member where minimal material, minimal layers and minimal contours (i.e., bends in the laminates) are all advantageous. Unfortunately, providing a configuration that uses minimal laminate material, requires minimal layering and restricts the laminate to a single plane is extremely difficult given the sink member configurations required to minimize overall configuration size and provide essentially uniform heat dissipating capacity to all switching devices mounted to the sink. For example, where devices are arranged in rows and columns to provide similar distances between channel inlets and devices down stream therefrom, typically a large number of laminate layers and a correspondingly complex labyrinth of vias are required to link components together. As another instance, where switching device lengths are aligned with similarly dimensioned capacitor lengths the lamination bus typically requires one or, more often, several bends to accommodate connection terminals that reside in disparate planes. In either of these two cases (i.e., many layers or several laminate bends) the amount of material required to configure a laminated bus bar can be excessive and hence unsuitable for certain applications.
Yet one other cost consideration related to converter configurations has to do with component versatility or the ability to use converter components in more than one converter configuration. Component versatility is particularly important with respect to the more expensive component types such as, for example, the heat sink assembly, the laminated bus bar, etc. In this regard, overall system costs can be reduced by designing sinks and laminated bus bars that can be used with various device and capacitor types. For instance, assume that a first converter configuration includes a first type of switching device, a first type of capacitor, a first type of sink member and a first type of laminate bar. Also assume that the sink, devices and a capacitors are dimensioned such that when the capacitors and devices are mounted to the sink, the capacitors connection terminals are on the same plane as the device connection terminals. Here, the first laminate bus bar type can be planar and hence relatively.
Next assume that a designer wants to swap out a second capacitor type for the first type in the configuration where the second capacitor type has a thickness between its dissipating surface and its connection terminals that is different than a similarly measures thickness of the first capacitor type. In this case, when the capacitors are swapped, the capacitor and device terminals will no longer reside within the same plane and a different, perhaps custom designed, laminate will be required to accommodate the change. In the alternative, the sink design may be altered to accommodate the change in device and capacitor terminal planes although this solution would be relatively expensive. Similar problems occur when different switching devices are swapped into configurations.
Thus, it would be advantageous to have a heat sink assembly that is relatively inexpensive to manufacture and yet provides substantially similar heat dissipating capacity to all devices mounted thereto. In addition, it would be advantageous if a sink assembly of the above kind could be used with a simplified laminate design and be used to configure relatively compact converter assemblies. Moreover, it would be advantageous if the sink assembly could be versatile and hence used with other converter components that have many different dimensions.
It has been recognized that relatively compact and inexpensive converter configurations can be configured by using an elongated liquid cooled heat sink to cool power switching devices. More specifically, it has been recognized that, where switching devices are mounted in a single row to a sink member mounting surface, the sink can be used to configure minimal volume converter configurations. In at least one embodiment of the invention, the sink mounting surface has a width dimension that is substantially similar to a width dimension of switching devices to be mounted thereto with the device width dimensions aligned with the mounting surface width dimension. This single row limitation has several configuration advantages described below.
It has also been recognized that, with certain types of refrigerant, the cooling capacity differential along a cooling channel appears to be exacerbated along the channel length. For instance, the cooling capacity differential appears to be relatively pronounced in the case of two phase refrigerants such as R-134a and R-123. As the label implies, two phase refrigerants change from a liquid to a gas when heat is absorbed and hence, generally, absorb a greater amount of heat, due to the endothermic nature of the phase change, than conventional single-phase liquid refrigerants such as waterxe2x80x94hence two phase refrigerants are generally preferred in high efficiency heat sinks.
Moreover, it has been recognized that, unfortunately, as two-phase refrigerants absorb heat and change phase from liquid to gas, vapor bubbles are formed within the liquid that accumulate on the internal surfaces of the heat sink and form gas pockets. The gas pockets on the surface of the channel block refrigerant from contacting the channel surface and hinder device heat absorption by the refrigerant. Thus, the channel surfaces on which gas pockets form end up becoming hot spots on the channel surfaces and the temperatures of devices attached adjacent thereto rise.
Because the vapor bubbles are formed by heat absorption and because coolant relatively further down stream from an inlet is warmer than coolant more proximate the inlet, relatively more vapor bubbles are formed down stream from the inlet than proximate the inlet thereby causing more gas pockets to form down stream which increases the temperature differential along the channel length. Thus, it has been determined that, while coolant temperature accounts for some of the temperature differential along a coolant channel length, much of the temperature differential is actually due to different amounts of gas accumulating along different sections of the channelxe2x80x94the gas having an insulating effect between the channel surfaces and the coolant passing thereby. Based on these realizations it should be appreciated that the temperature differential problem is exacerbated where sink channels are extended.
According to several embodiments of the invention, protuberances of a character, quantity and size that increase turbulence within sink channels to a point where the turbulence either prohibits gas pockets from forming on the channel surfaces or dislodges or breaks up gas pockets that form on the channel surfaces, are provided on at least one of the channel surfaces. It has been found that when such protuberances are provided within a channel, the channel can have an extended length without causing excessive temperature differentials there along. More specifically, it has been determined that the channel length can, in at least one embodiment, extend substantially along an entire sink length where the sink, as indicated above, has a length to accommodate a single row of switching devices. For instance, where a converter configuration includes twenty four switching devices, the twenty four devices can be arranged in a single row along the sink member mounting surface where the channel extends along substantially the entire sink length from an inlet to an outlet.
It has also been determine that, in at least some embodiments of the invention, the sink member can be juxtaposed so that the channel inlet is below the channel outlet and, more specifically, so that the channel inlet is directly vertically below the channel outlet. Here, dislodged or broken up gas pockets, being lighter than the refrigerant, are aided by buoyancy in their movement toward the outlet at the top of the sink channel.
By providing an elongated sink-device assembly including devices mounted in a single row to an elongated sink member, overall converter cost can be reduced. In this regard, the single channel sink member can be manufactured using the two piece sealing method described above where the channel is bore out of a body member, a cover member is hermetically sealed over the channel and inlet and outlet ports that open into the channel are formed.
In addition, cost is reduced with the inventive elongated sink-device assembly as a simplified laminated bus bar can be used with the sink-device assembly. In this regard, where capacitors are juxtaposed to one side of the switching devices and with capacitor terminals and device terminals positioned within a common connection plane, the distances between capacitor terminals and the device terminals that the capacitor terminals are to be linked to are reduced appreciably so that less material is required to make terminal connections. Moreover, because capacitor terminals and the device terminals to which the capacitor terminals are to be linked may be positioned proximate each other, none of the laminates have to pass over other devices disposed intermediate the connecting terminals and therefore simpler laminate and associated via designs can be employed that include relatively small numbers (e.g., 3) of laminate layers.
Consistent with the above, at least some embodiments of the invention include an apparatus for sinking heat away from a plurality of power switching devices where each power switching device includes a heat dissipating surface having a dissipating width dimension and having a device length dimension perpendicular to the dissipating width dimension, the apparatus comprising a heat sink member having a sink length dimension between inlet and outlet ends, forming an internal channel that extends substantially along the entire sink length dimension and also forming inlet and outlet ports that open into the channel at the inlet and outlet ends, respectively, the sink including first and second oppositely facing surfaces, the second surface for receiving the heat dissipating surfaces of the power switching devices, the second surface having a receiving width dimension that is substantially perpendicular to the sink length dimension and that is less than twice the device dissipating width dimension.
In some embodiments the receiving width dimension is substantially similar to the dissipating width dimension. In some embodiments the receiving width dimension is defined by the channel. Each switching device includes a device mounting surface. The mounting surface may include the device dissipating surface and may form a device width dimension that is larger than the dissipating width dimension, the dissipating surface may include the portion of the mounting surface from which heat is dissipated.
More specifically, the sink member may form a sink width dimension that is substantially parallel to and greater than the receiving width dimension and wherein the sink width dimension and the device width dimension are substantially similar. The sink length dimension may be substantially similar to the combined lengths of the power switching devices.
When the power switching devices are aligned end to end to form a device row with first and last devices at either end of the device row, oppositely facing edges of the dissipating surfaces of the first and last devices may define a dissipating length and channel length may be substantially similar to the dissipating length. Some embodiments may further include at least one divider member formed in the channel and that extends substantially from the inlet end to the outlet end thereby dividing the channel into at least first and second substantially parallel channels.
At least some embodiments further include second and third divider members juxtaposed on opposite sides of the one divider member and that further divide the first and second channels into inner and outer fist channels and inner and outer second channels, respectively, each of the second and third dividers forming openings between the respective inner and outer channels. Here, the openings may be substantially equi-spaced along the lengths of the second and third divider members. In addition, the divider member may be substantially perpendicular to the second surface.
In some embodiments the divider member extends to the inlet end of the channel and the sink member also forms a manifold chamber between the inlet and the channel, the manifold chamber opening into the first and second channels through first and second nozzles, respectively. The divider member may terminated prior to the outlet end so that the first and second channels come together at the outlet end.
Each device includes first and second mounting flanges that form portions of the mounting surface and that are separated by the dissipating surface, each mounting flange having a flange width dimension. Here, the sink may include a lateral wall member on either side of the channel having a wall thicknesses that is substantially similar to the flange width dimensions. Also, here each mounting flange may form at least one flange mounting aperture and wherein the lateral walls form wall mounting apertures that align with the flange apertures and the apparatus may further include a separate securing member for each of the flange/wall aperture pairs.
In some embodiments the sink member includes a body member and a cover member, the body member forming the second sink surface, including a first body member surface facing in a direction opposite the second surface and forming a cavity in the first surface, the cover member including at least a first cover surface, one of the cover member and the body member forming the inlet and one of the cover member and the body member forming the outlet, the cover member first surface hermetically sealed to the body member first surface to enclose the cavity and form the sink channel.
Some inventive embodiments include a power brick apparatus comprising a plurality of power switching devices, each device including a heat dissipating surface having a dissipating width dimension and having a device length dimension perpendicular to the dissipating width dimension and a heat sink member having a sink length dimension between inlet and outlet ends, forming an internal channel that extends substantially along the entire sink length dimension and also forming inlet and outlet ports that open into the channel at the inlet and outlet ends, respectively, the sink including first and second oppositely facing surfaces, the second surface for receiving the heat dissipating surfaces of the power switching devices, the second surface having a receiving width dimension that is substantially perpendicular to the sink length dimension and that is less than twice the device dissipating width dimension, wherein, the power switching devices are mounted end to end so that their combined length extends along the sink length.
In addition, several embodiments of the invention include a method for sinking heat away from a plurality of power switching devices where each power switching device includes a heat dissipating surface having a dissipating width dimension and having a device length dimension perpendicular to the dissipating width dimension, the method comprising the steps of providing a body member having a sink length dimension between inlet and outlet ends, having first and second oppositely facing surfaces, the second surface having a receiving width dimension that is substantially perpendicular to the sink length dimension and that is substantially similar to the device dissipating width dimension, forming a cavity in the first surface of the body member that extends substantially along the entire sink length dimension, providing a cover member, forming an inlet in one of the body member and the cover member, forming an outlet in one of the body member and the cover member, hermetically sealing the cover member to the first surface of the body member so that the cover member and cavity together form a channel and so that the inlet and outlet open into opposite ends of the channel and mounting the devices to the second surface with the dissipating width dimensions substantially parallel to the receiving width dimension.
Here, each of the devices may include connector leads that extend to one side of the device and the step of mounting may include mounting all of the devices to the sink member with all of the leads extending to one side of the sink member and in a direction substantially perpendicular to the sink length dimension. In addition, in some embodiments, the step of forming the channel includes forming four substantially parallel channels that are separated by divider members that are substantially perpendicular to the second surface the divider members including a first divider member that is disposed between a second and a third divider member and providing openings between adjacent channels and through the second and third divider members.
In some embodiments the step of providing the channels further includes providing the first divider member so as to extend to the inlet end of the channel and wherein the method further includes the step of forming a manifold chamber between the inlet and the channel, the manifold chamber opening into the first and second channels through first and second nozzles, respectively.